Re: [PATCH v3 1/2] qcow2: Report BDRV_BLOCK_ZERO more accurately in bdrv_co_block_status()

[Vladimir Sementsov-Ogievskiy]

10.09.2020 20:46, Alberto Garcia wrote:

If a BlockDriverState supports backing files but has none then any
unallocated area reads back as zeroes.

bdrv_co_block_status() is only reporting this is if want_zero is true,
but this is an inexpensive test and there is no reason not to do it in
all cases.

Suggested-by: Vladimir Sementsov-Ogievskiy 
Signed-off-by: Alberto Garcia 


Reviewed-by: Vladimir Sementsov-Ogievskiy 


---
  block/io.c | 8 
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/io.c b/block/io.c
index ad3a51ed53..1b0ae29610 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2408,16 +2408,16 @@ static int coroutine_fn 
bdrv_co_block_status(BlockDriverState *bs,
  
  if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {

  ret |= BDRV_BLOCK_ALLOCATED;
-} else if (want_zero && bs->drv->supports_backing) {
-if (bs->backing) {
+} else if (bs->drv->supports_backing) {
+if (!bs->backing) {
+ret |= BDRV_BLOCK_ZERO;
+} else if (want_zero) {
  BlockDriverState *bs2 = bs->backing->bs;
  int64_t size2 = bdrv_getlength(bs2);
  
  if (size2 >= 0 && offset >= size2) {

  ret |= BDRV_BLOCK_ZERO;
  }
-} else {
-ret |= BDRV_BLOCK_ZERO;
  }
  }
  




--
Best regards,
Vladimir

[PATCH v3 1/2] qcow2: Report BDRV_BLOCK_ZERO more accurately in bdrv_co_block_status()

[Alberto Garcia]

If a BlockDriverState supports backing files but has none then any
unallocated area reads back as zeroes.

bdrv_co_block_status() is only reporting this is if want_zero is true,
but this is an inexpensive test and there is no reason not to do it in
all cases.

Suggested-by: Vladimir Sementsov-Ogievskiy 
Signed-off-by: Alberto Garcia 
---
 block/io.c | 8 
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/io.c b/block/io.c
index ad3a51ed53..1b0ae29610 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2408,16 +2408,16 @@ static int coroutine_fn 
bdrv_co_block_status(BlockDriverState *bs,
 
 if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {
 ret |= BDRV_BLOCK_ALLOCATED;
-} else if (want_zero && bs->drv->supports_backing) {
-if (bs->backing) {
+} else if (bs->drv->supports_backing) {
+if (!bs->backing) {
+ret |= BDRV_BLOCK_ZERO;
+} else if (want_zero) {
 BlockDriverState *bs2 = bs->backing->bs;
 int64_t size2 = bdrv_getlength(bs2);
 
 if (size2 >= 0 && offset >= size2) {
 ret |= BDRV_BLOCK_ZERO;
 }
-} else {
-ret |= BDRV_BLOCK_ZERO;
 }
 }
 
-- 
2.20.1